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Alvin: The little submarine that could

Scientists take Alvin to the ocean floor in the Cayman Trench in the Caribbean Sea in 2008.National Geographic/Getty Images

As the world races to outer space, a submarine about the size of a delivery truck has explored what some consider the real final frontier: the deep blue sea.

The first research submarine capable of carrying passengers to and from the seafloor, Alvin has spent some 50 years plumbing the ocean's depths. Although not as sleek or sexy as the Space Shuttle, the tubby white submersible has responded to national crises — even recovering a lost hydrogen bomb — and discovered extreme ecosystems that challenged long-held ideas of where life is possible.

Woods Hole Oceanographic Institute scientist Allyn Vine set the gears in motion for a manned research submersible in the 1950s during a symposium on deep-sea study. The problem? Existing submarines couldn't dive deep enough or transport passengers. Onboard instruments could take measurements, of course, but "people are so versatile," Vine said. "I find it difficult to imagine what kind of instrument should have been put on the Beagle instead of Charles Darwin."

So six years later, WHOI contracted General Mills to build a research submarine that could safely shuttle a pilot and two scientists 6,000 feet underwater and back to the surface. Officially commissioned in June 1964, the 35,200-pound submarine named Alvin — a portmanteau of Vine's first and last names — holds enough air to sustain crewmembers for up to three days as they observe their surroundings from the cockpit and control robotic arms to collect organisms, sediments and other samples.

Two surplus Navy pontoons formed a makeshift catamaran — dubbed Lulu, after Vine's mother — to support Alvin during its dives. After a year of test dives, Alvin completed its first mission in 1966: finding and retrieving a hydrogen bomb that had plummeted into the Mediterranean when a U.S. B-52 carrying the bomb collided with a tanker near Spain.

But Alvin landed in some sticky situations, too, from tangling with a swordfish (which was later pulled ashore and eaten for dinner) to losing an arm. In 1968, the steel cables that tethered Alvin to Lulu snapped, and it sank 5,000 feet, where it remained before being recovered nearly a year later. Fortunately, no one was inside and Alvin itself was incredibly well-preserved; its structure almost entirely intact, the apples and bologna sandwiches in its cockpit discolored but still edible.

In 1977, Alvin discovered piping-hot vents teeming with giant clams, red-plumed tubeworms and other strange creatures along the Galapagos Rift. Until then, scientists believed that deep-sea animals fed on organic matter that had fallen from the surface, after absorbing the sunlight that land life depends on for energy. But they realized that these so-called extremophiles rely on chemosynthesis, a process that converts methane and other chemicals (instead of sunlight) into energy — expanding their understanding of where life could exist.

After snapping the first photos of the Titanic wreckage in 1986, Alvin underwent upgrades and continued to explore chemosynthetic ecosystems, from a whale skeleton crawling with tubeworms and other creatures to an eerie terrain of 60-foot-tall white carbonate rock pinnacles along the Mid-Atlantic Ridge (aka the Lost City). Alvin came to the national rescue again in 2010, when it evaluated damage from the BP oil spill in the Gulf of Mexico. Scientists onboard photographed dead and dying corals, stripped of living tissue and coated in tufts of dark oil.

Alvin's pilots, of course, deserve kudos. Like astronauts, many hold engineering degrees and also undergo stringent training, including a series of tests to earn U.S. Navy certification. One test requires them to draw Alvin's hydraulic, electrical and other components — all from memory. They're mechanics, too, responsible for fixing any malfunctions during a dive.

Throughout 2011 into 2013, after more than 4,600 dives, Alvin underwent a massive upgrade. "We basically redesigned and rebuilt the entire vehicle," said Pat Hickey, who headed the Alvin Operations Group during the overhaul. Earlier this year, the submersible returned to the Gulf of Mexico, where pilots and scientists are continuing to test its new battery capacity, HD cameras and maneuverability.

Some scientists have used Alvin's discoveries to make a case for exploring the ocean, often considered less glamorous than space; NASA's budget was about $17 billion in 2013, but only $5 billion funds ocean exploration. Yet 95 percent of the ocean remains unexplored, and we have better maps of the surface of Mars than we do of our seafloor.

The more we understand the deep sea, the better we can conserve its inhabitants, from the fish that 1 in 5 people use as a primary protein source to the algae and other organisms that could be used to make life-saving pharmaceuticals. And Alvin isn't through yet. Its upgrades are expected to yield even more surprising discoveries that will lure scientists toward the deep blue abyss.